Pharamcology Principles Flashcards
Three phases of drug action
1: pharmaceutic phase
2: pharmacokinetics phase
3: pharmacodynamics phase
Pharmaceutical phase
The breakdown of tablets into smaller and smaller particles that can be absorbed in the blood
- only for PO drugs
- must occur to be absorbed
Pharmacokinetics phase
What happens to the drug in the body after it has been broken down and absorbed
- drug absorbed by SI, enters blood and transported to sites of action
- four processes: absorption, distribution, metabolism/biotransformation, excretion
Drugs and phospholipid bilayer
Cell membranes are composed of lipids, so only lipid soluble compounds can easily migrate across
- we make drugs lipid soluble
- water soluble drugs are transported by membrane channels or pores
absorption
First pass effect
Refers to the metabolism of the drug in the liver before entering systemic circulation
-liver breaks down certain percentage of drug into bioavailable form (active) —the amount of drug left after first pass
- PO: bioavailability varies
-IV: bioavailability is 100%
absorption
Routes of absorption
1) enteral
2) prenteral
3) topical
Enteral absorption
GI tract (oral/gastric mucosa, SI, rectum)
- EC (enteric coated, breakdown and absorption in SI) (first pass)
- PO (breakdown in stomach, absorbed in SI (first pass effect
- SL, buccal, rectal (highly vascular. So no first pass)
Parenteral absorption
SQ, IM, IV, intrathecal (spinal cord), epidural (dural space)
- IV is fastest
- none are first pass
Topical absorption
Application of meds to body surfaces
- eyes, skin, ears, nose, lungs
- slower onset, no first pass bc localized
Distribution in pharmacokinetics phase
The movement of drug through the body and the process of drugs leaving blood and entering site of action
- depends largely on adequacy of blood circulation bc drug has easier time getting to site
Examples of disruption of distribution in pharmacokinetics phase
- peripheral vascular disease
- abscesses
- tumors
- drugs can’t get to site of action to heal *
Blood brain barrier (BBB)
Tight junctions of the capillary walls endothelial cells
- prevent easy passage of drugs
- drugs need transport system or extremely lipid soluble
- alcohol, glucose can pass
protein binding effect
Purpose: temporarily store drug molecules so they are available for longer periods of time which helps maintain steady free drug conc
- reversible process
- drugs must be unbound to exert effect
- albumin is primary plasma protein that binds drugs
drugs can be high protein bound or low
Hypoalbuminemia
Low protein levels (albumin)
- allows for increase in free drugs which risk possibility of overdose/toxicity
- ex: warfarin
Metabolism of pharmacokinetics
Biotransformation — drugs are inactivated in liver into metabolites
- lipid soluble to water soluble
- performed by cytochrome P-450
importance: if liver is not working, drugs are not inactivated, risk toxicity
Cytochrome P-450 (aka CYP450)
Group of isoenzymes that metabolize drugs
- metabolize 1/2 of all drugs
- drug - drug interactions can occur when taken concurrently
Types of CYP450
- substrate: drug uses CYP450 for metabolism, converts active forms
- inducer: speeds of CYP450 (increases breakdown), decreases drug and therapeutic effect
- inhibitor: inhibits CYP450 (decreases breakdown), increases drug and risk toxicity
Excretion of pharmacokinetics
Elimination of drugs from the body by the kidneys
- generally hydrophilic (water soluble) drugs
- some drugs are reabsorbed (renal tubules)
Effects of kidney disease on excretion
Drugs are not excreted and can build up causing toxicity
- check with renal labs (blood urea N, creatinine)
- glomerular filtration rate: best measure of kidney function (related to free drug conc in plasma)
Half life:
Serum half-life: time required for serum conc to decrease by 50%
- takes 5 half lives to be 97% eliminated
- about 4-5 half lives for steady state to occur which is when the drug = amount metabolized/excreted
- dictates dosage, frequency
Around the clock dosing (ATC)
Goal to maintain 50% drug conc in body
- used to treat chronic pain
- PRN for breakthrough pain
Onset
Time it takes for drugs to elicit therapeutic response
Peak
Time it takes for drugs to reach max therapeutic effect
duration
Time drug conc is sufficient to elicit a therapeutic response
Pharmacodynamics
What the drug does in the body like increase, decrease, replace, inhibit, destroy, protect, or irritate to CREATE A RESPONSE
- drugs exert multiple effects on body (some desired some not)
- ex: slide 64 metaproterenol
Importance of receptors
Receptors are found on cell membrane surface and composed of proteins
- chemical (drugs) will bind to create drug-receptor complex that will produce effects
- categorized as agonist/antagonist
some drugs don’t need receptors and act with simple physical/chemical interactions
Agonist
Drug with ability to initiate desired therapeutic effect when binding
- occupy receptor and activate
- ex: drug binds causing vasodilation to lower peripheral vascular resistance
Antagonist
Drug that binds and prevent/block/inhibits other ligands from binding so not response is activated
- occupy receptor and block
- ex: Zantac blocks release of gastric acid
Therapeutic index
Amount of drug needed in the body to have an effect and not be at toxic levels
- measures relative safety of drug
Narrow therapeutic index
Ratios with lowest conc of drug at which clinical toxicity can occur
Black box warning
FDA warning that drug is especially dangerous
- strongest safety warning and still remain in market
- must have warning on package insert, product label, advertising
Processes to prevent med errors
-restrict high alert meds and med routes
- drug differentiation (using tall-man)
- computerized admin
- pt info accessible
- standardize and simplify
- apply reminders
- include pt in therapy
- don’t use trailing zeros
- use leading zeros
High alert medications
Meds most likely to cause serious harm
- insulin, heparin, opioids, injectable potassium chloride, neuromuscular blocking agents, chemo drugs
Drug interactions
-drug- drug
-drug- food
-drug- herb
-drug- disease
Ways nurse can minimize drug interactions
-decrease number of drugs
-through drug history
-extra vigilant monitoring narrow therapeutic index
Drug interactions that increase therapeutic effect
- additive effects
- synergism/potentiation
- activation
- displacement
Additive effects
2 drugs with similar MOA that make stronger effect
Synergism/potentiation
2 drugs w diff MOA but combine have greater effect than either drug alone
Activation
Drug metabolizing enzyme in liver that decrease CYP450, so decrease metabolism rate
-purposely altering metabolism
Displacement
Displacement of one drug from plasma protein binding sites by a second drug increases effect of displaced drug
- how much drug is available due to protein binding
Drug interactions that decrease therapeutic effects
-antidote
-decrease intestinal absorption
- activation
Antidote
Given to antagonize toxic effects of another drug
Decrease intestinal absorption
In relation to PO meds, does pt have healthy intestines to break down drugs and absorb
Activation
Activating drug metabolizing enzymes in the liver to induce
- increase metabolism rate (quicker out of body)
- CYP450 system
Consideration for older adults and pharmacokinetics
- hepatic changes: drugs metabolize slower
- gastrointestinal changes: decrease absorption of oral drugs
- cardiac and circulatory changes: impaired circulation means decreased distribution of drugs
- renal changes: drugs are excreted less completely
